Method for monitoring proper fastening of an article of assembly at more than one location

ABSTRACT

A more reliable and fool-proof method and apparatus for assembling an article of assembly (e.g. with predetermined screw torque requirements) in which the article of assembly has multiple fastening locations. The method comprises holding the article of assembly fixed while providing at least two different types of targets fixed relative to the article of assembly that correspond to the individual fastening locations. Fasteners are fastened into the article of assembly at the fastening locations. When fastening is occurring at one of the fastening locations, one of the targets is being sensed. Based on the target sensed, a target output is generated that differentiates between different types of targets thereby indicating fastening location of the fastening tool. The electronic target output is used for electronic control such as for stopping a conveyor to keep the article of assembly at an assembly station until the fastening operations have been completed.

CROSS-REFERENCE TO RELATED PATENT APPLICATIONS

[0001] This patent application is a divisional of copending U.S. patentapplication Ser. No. 09/992,326, filed Nov. 19, 2001, pending.

FIELD OF THE INVENTION

[0002] The present invention relates generally to assembly systems, andmore particularly relates to monitoring fastening of articles ofassemblies in such assembly systems.

BACKGROUND OF THE INVENTION

[0003] There are many industries where the sequence of fasteningoperations and/or the applied torque of fastening operations arecritical in assembling an article of assembly. One such particularindustry is the automotive seat assembly industry.

[0004] In the automotive seat assembly industry, if the fasteningoperation of screws on a seat frame is not performed correctly to fastenthe parts of the seat together, then the assembled seat may be moreprone to possible failure. Proper fastening of a screw may require apredetermined amount of torque to be applied to one or more screws orthat the screws be fastened according to a predetermined sequence, orpossibly both requirements. It is also necessary that all of thefastening locations be properly subject to a fastening operation andfilled with a fastener.

[0005] A common requirement in the seat industry is that certaincritical screws need to be fastened with a predetermined amount oftorque. The amount of torque required for different screws among a seatcan also sometimes be different. Screw torque requirements can be socritical for certain industries that monetary fines or disqualificationof manufactured product can occur if certain critical screws that havenot been properly fastened or torqued to the predetermined value.

[0006] In seat assembly operations, it is desirable to assembly a largevolume of seats on an assembly line. In modern systems, this istypically accomplished with conveyor systems that carry seats held infixtures through multiple assembly stations. Conveyor systems may be acontinuously moving line whereby seats are worked on and assembled asthe seats are moving and traveling down the line, or as an intermittentstop and go system whereby seats are temporarily stopped at each stationfor assembly operations and then conveyed down the line to the nextstation. At the stations where seat parts are assembled with screwsaccording to a predetermined torque, torque reaction arm drivers areused. Torque reaction arm drivers provide an indication of the amount oftorque applied during a fastening operation.

[0007] To achieve high volume assembly and to keep conveyor lines short,typically several different screws are fastened by a single worker at agiven assembly station along the line. For example, a common arrangementis a seat assembly station where several screws are installed into theseat requiring a predetermined applied torque of the same value. Thissystem includes a mechanism that keeps a seat at a station until thedesired number of torque values is achieved with the torque reaction armthat is equal to the number of screws being installed.

[0008] While the torque reaction arm is capable of providing anindication of driven torque, this type of system can be easily trickedor subject to failure. In particular, if the worker of the torquereaction arm drives the same screw twice he can accidentally provide twotorque values for one screw. In repetitive work operations requiringseveral tasks at a single assembly station, workers can forget whichscrew has been properly fastened or otherwise make an accidental errorin fastening the same screw twice. The result is that one or more screwshave been improperly fastened despite the total number of torque valueshas been achieved for the station (thereby allowing release of the seatfrom the station for further downstream assembly).

[0009] Even without mistakes, some workers have been known tointentionally bypass or trick existing systems. In particular, therehave been instances where a worker drives a screw, then reverses thesame screw and then refastens that same screw at the same location toget more than one good output value at the same location to in effecttrick the system. Workers have even been known drive a screw mounted ina panel proximate the assembly station to intentionally bypass or trickthe system. The cause of these problems is difficult to understand butit may include worker frustration or fatigue with respect to properlyfastening screws into a seat.

[0010] One approach to reducing employee mistakes in fasteningoperations is to reduce the number of tasks performed at a given workstation. However, this approach increases the length and cost of theassembly line and decreases worker efficiency. Another approach is toinstall quality control in the form of close supervision or downstreamtorque checking to ensure quality and accuracy of fastening operations.However, increased supervision also increases costs and decreasesoverall efficiency of an assembly line. There have even been instanceswhere companies have discovered such fastening problems of a large scalelevel and have had to conduct massive quality control operations bymanually checking the proper installation of fasteners and thousands oftorque values on seats that have already been run through the line. Thisis both time consuming and costly.

BRIEF SUMMARY OF THE INVENTION

[0011] In light of the above, it is a general aim of the presentinvention to provide a more reliable and more fool-proof way to conductfastening operations in assembling an article of assembly.

[0012] In that regard, it is also a further object of the presentinvention to provide a more efficient way of ensuring fasteningoperations are performed correctly on an article of assembly.

[0013] In accordance with these and other objectives, the presentinvention is directed towards a new more reliable method for assemblingan article of assembly in which the article of assembly having multiplefastening locations in spaced apart relation. The method comprisesholding the article of assembly in a fixed position while providing atleast two different types of targets fixed relative to the article ofassembly that correspond to the individual fastening locations.Fasteners are fastened into the article of assembly at the variousfastening locations. When fastening is occurring at one of the fasteninglocations, one of the targets is being sensed. Based on the targetsensed, an electronic target output is generated that differentiatesbetween the different types of targets thereby indicating fasteninglocation of the fastening tool. The electronic target output can be usedfor electronic control or alarm purposes.

[0014] The present invention is also directed toward an assembly systemfor assembling articles of assembly to implement the above method. Theassembly system comprises a fixture holding the article of assembly, andfirst and second targets fixed relative to the fixture that correspondto first and second fastening locations on the articles of assembly. Afastening tool is adapted to fasten fasteners into the article ofassembly at the first and second fastening locations with different toolpositions relative to the fixture when the tool is at the differentfastening locations. The assembly system further includes a targetsensor fixed relative to the fastening tool along at least one axis. Thetarget sensor senses the first second targets when the fastening tool isfastening at the first and second locations respectively. The targetsensor generates a target output differentiating between the first andsecond targets and thereby indicates when the fastening tool the firstand second fastening locations.

[0015] Further aspects of the present invention relate toimplementations on conveyor systems including both continuous andnon-continuous or intermittent type conveyor systems.

[0016] Other objectives and advantages of the invention will become moreapparent from the following detailed description when taken inconjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0017] The accompanying drawings incorporated in and forming a part ofthe specification illustrate several aspects of the present invention,and together with the description serve to explain the principles of theinvention. In the drawings:

[0018]FIG. 1 is an isometric and partly schematic view of a seatassembly station according to a preferred embodiment of the presentinvention.

[0019]FIG. 2 is a side elevation view of the seat assembly stationillustrated in FIG. 1.

[0020]FIG. 3 is front elevation view of the seat assembly stationillustrated in FIG. 1.

[0021]FIG. 4 is a schematic flow/control diagram for an continuousmoving line conveyor type seat assembly station.

[0022]FIG. 5 is a schematic flow/control diagram for an intermittenttype seat assembly station.

[0023]FIG. 6 is an illustration of one type of sensing system for use inan embodiment of the present invention.

[0024]FIG. 7 is an illustration of another type of sensing system foruse in an embodiment of the present invention.

[0025] While the invention will be described in connection with certainpreferred embodiments, there is no intent to limit it to thoseembodiments. On the contrary, the intent is to cover all alternatives,modifications and equivalents as included within the spirit and scope ofthe invention as defined by the appended claims.

DETAILED DESCRIPTION OF THE INVENTION

[0026] For purposes of illustration, a preferred embodiment of thepresent invention has been illustrated in FIGS. 1-4 as embodied in anassembly station 10 for assembling articles of assembly illustrated inthe form of automotive seats 12. Although only one assembly station 10is fully illustrated in FIGS. 1-3, it will be appreciated that theassembly station 10 is one of several assembly stations that aretypically disposed in a predetermined sequence whereby assembly workoperations are performed.

[0027] To transport the seats 12 through the various stations, aconveyor 14 is provided that runs through the assembly station 10. Theconveyor 14 is illustrated as a continuous type in which the conveyor 14runs and moves the seats 12 substantially continuously. In particular,the conveyor 14 will typically run on a continuous basis andcontinuously move the seats 12 downstream through the various stationsunless the necessary work operations any of the particular stations arenot performed within the allotted time given for that station, or abreakdown occurs, or other similar event occurs requiring stoppage ofthe conveyor 14. As can be seen in FIG. 1, the assembly station 10 has aspan 16 of work area over which the work operations can be performed atthe illustrated assembly station 10. The amount of time a seat 14typically spends at an assembly station is equal to the length of thespan 16 divided by the operating speed of the conveyor 14.

[0028] The conveyor 14 includes a stationary support frame 20 and amoving line 22. A plurality of seat fixtures 18 are affixed to themoving line 22 at equidistant intervals. The seat fixtures 18 clamp ontoor other wise hold the seats 12 in a fixed position for assemblyoperations. Unassembled base frames of seats 12 are clamped into thefixtures 18 (typically through locating pins and a clamping mechanismthat are not shown) at the upstream input location of the conveyor 14,while assembly seats are removed from the fixtures 18 at the downstreamoutput location of the conveyor 14. The fixtures 18 are recycled andused over and over again for assembling seats 18.

[0029] For purposes of reference, three mutually perpendicular axes 24,26, 28 have been shown. The axes include a horizontal axis 24 parallelto the conveyor 14, a vertical axis 26 and a tool plunging axis 28.

[0030] At the illustrated assembly station 10, a fastening tool isprovided in the illustrated form of an electrically powered, torquereaction arm, screw driver 30 (“power screw driver”) for drivingthreaded bolts, screws or other threaded fasteners into the frame 13 ofthe seat 12. The power screw driver 30 is manually operated including ahandle 32 and a trigger 34 that provides for forward and reverse modesto correspondingly drive or remove threaded fasteners. The power screwdriver 30 also comprises an integral torque monitor 31 that is capableof providing an output of the torque applied to fasteners by the powerscrew driver 30.

[0031] The power screw driver 30 is mounted on a horizontal toolplatform 36 via a first linear rail mechanism 38 that extends the toolplunging axis 28. The first linear rail mechanism 38 allows for slidinglinear movement of the driver 30 in the plunging axis 28. The horizontaltool platform 36 is in turn supported by a second linear rail mechanism40 that extends in the vertical axis 26. The second linear railmechanism 40 is mounted to a vertical support plate 42. The secondlinear rail mechanism 40 allows for sliding linear movement of thedriver 30 in the vertical axis 26. A supporting recoil cylinder 44 maybe used to support the horizontal platform 36 at the desired height andto counteract the force of gravity for the support assembly of thedriver. The vertical support plate 42 is in turn supported by a thirdlinear rail mechanism 46 that is mounted to an adjacent wall or side 48of the conveyor 14. The third linear rail mechanism 46 allows forsliding linear movement of the driver 30 in the horizontal axis 26parallel to the length of the conveyor 14 at the assembly station 10.The length of the third linear rail mechanism 46 also determines andsets the span 16 of the assembly station 10 over which fasteningoperations can be performed with the power screw driver 30. From theforegoing, it can be seen that the power screw driver 30 can bemanipulated along the three different axes 24, 26, 28, relative to theconveyor 14 and or fixtures 18 to fasten screws into seats 12 asdesired.

[0032] In accordance with the present invention, the disclosedembodiment includes a plurality of differentiated targets 50 a, 50 b, 50c corresponding to different fastening locations 52 a, 52 b, 52 c on theseat 12, respectively, and a target sensor in the form of a machinevision camera 54 for sensing the targets 50 a-c. The camera 54 is fixedrelative to the power screw driver 30 in at least one axis, up to allthree axes. For example the target sensor camera 54 may be mounted tothe horizontal platform 36 and is therefore fixed relative to the powerscrew driver 30 in the vertical and horizontal axes 24, 26.

[0033] The individual targets 50 a-c are fixed relative to the seat 12in spaced apart relation to their respective fastening locations 52 a-con the seat 12. The spaced apart relation is substantially the samebetween each of the targets 50 a-c and corresponding fastening locations52 a-c in terms of distance (horizontal and vertical) and angularorientation. This equidistant spacing is also substantially the same asthat between the tip end of the power screw driver 30 and the machinevision camera 54. In this manner, and with the camera 54 alignedparallel to the tool plunging axis 28, the machine vision camera 54 willsense the first target 50 a when the power screw driver 30 is at thefirst fastening location 52 a, will sense the second target 50 b whenthe power screw driver 30 is at the second fastening location 52 b, andwill sense the third target 50 c when the power screw driver 30 is atthe third fastening location 52 c.

[0034] To fix the targets 50 a-c relative to the seat 18, the targets 50a-c are preferably provided on panels 56 that in turn are mounted to theeach one of the fixtures 18. The targets 50 a-c may also be mounted tothe moving line 22 of the conveyor (since the conveyor moves at the samespeed as the seats) or mounted to or integrally provided by the seats 18themselves to provide for fixed targets relative to the seats. Forintermittent stop and go systems, the targets may be fixed stationary atthe assembly station such as to the stationary support frame of theconveyor because the seat is stopped in position while work operationsare being performed.

[0035] As shown in FIG. 1, each of the targets 50 a-c has a distinctivecharacteristic that is different than that of the other targets 50 a-c,which allows for differentiation of the targets 50 a-50 c. In FIG. 1 thedistinctiveness is provided through different angular orientations of alarge bolt head target and a small bolt head target. The machine visioncamera 54 generates an electronic output that differentiates between thedifferent targets 50 a-50 c. This electronic output of the machinevision camera 54 is communicated to a processor or electronic controller58.

[0036] The electronic controller 58 has several outputs and inputs andcan utilize the electronic output from the machine vision camera 54 fora variety of purposes such as sounding an alarm, stopping the conveyor14 and/or collecting data for analysis or quality control purposes. Theactual purpose may vary between applications.

[0037] In continuous conveyor seat assembly systems where certain screwtorques or fastening sequences may be critical, the electronic outputfrom the machine vision camera 54 may be used to stop the conveyor 14 inthe event that not all fastening operations are performed correctly asrequired, to allow further time to finish those operations at theillustrated assembly station 10. Although this can stop the entireconveyor line and affect other upstream or downstream stations, thedisclosed embodiment ensures fool-proof assembly that ensures thatproper fastening torques at each of the fastening locations 52 a-cand/or fastening sequences at the fastening locations 52 a-c is achievedwith no further quality control required over fastening operations. Intypical assembly line set ups, the conveyor line 22 will be moving at aspeed that is typically sufficient to allow all work to be accomplishedin the allotted time at each of the assembly stations along theconveyor.

[0038] At the illustrated assembly station 10 of FIG. 1, the electroniccontroller 50 has an position sensor input indicating when seats 12enter and are about to leave the assembly station 10. This input mayinclude a first proximity sensor 60 located near the entrance to theassembly station 10 for indicating when a seat is about to enter thestation 10 and includes a second proximity sensor 62 located near theexit of the assembly station 10 for indicating when a seat is about toleave the station 10. The electronic controller 50 also has a connectionto the conveyor drive 64 that is operable to stop the moving line 22 ofthe conveyor 14. The electronic controller 50 also has a connection tothe torque reaction arm or driver 30 for activating the driver 30 whenthe driver 30 is in a proper fastening position and disabling the driver30 when the driver 30 is not in a proper position to fasten at one ofthe fastening locations 52 a-c. The electronic controller 50 alsoreceives feedback from a torque monitor 31 integral with the driver 30to provide an indication of the driven torque applied at a fasteninglocation.

[0039] For purposes of illustration, one form of an operationalelectronic control diagram with a continuous conveyor system isillustrated in FIG. 4. As shown in FIG. 4 with continuing crossreference with FIG. 1, a continuous conveyor system preferably includestwo different types of seat fixtures 18, 19 which hold the same seat butare differentiated by virtue of the fact that they have different typesof the first, second and third targets 50 a-50 c, 51 a-51 c. In thismanner, if the fixture spacing along the conveyor 14 is such that morethan one fixture may be at the assembly station 10 within its span 16 ata given moment, the machine may not be tricked by moving the driver 30from the seat of the leading fixture 18 to the seat of the trailingfixture 19 and fastening the location(s) that are missing from the seatheld in the leading fixture 18.

[0040] In any event, the program is started by first monitoring fixtureposition 100 in response to the fixture position sensor 62 to ensurethat the leading fixture 18 has not left the station 10 with a seat 12without proper fastening at each of the three fastening locations 52a-52 c. It is determined whether a fixture has left or is about to leavethe assembly station without proper fastening at all three locations(e.g. setting flags as will be described) 102. If not all fasteninglocations have been properly fastened, then the electronic controllersends a stop signal 104 to the conveyor drive 64 to stop the conveyor 14to ensure that all necessary fastening operations can be completed.

[0041] If, however, there is still time to conduct fastening operations,then the tool position is monitored 106 to determine whether thefastening tool or driver 30 is at a fastening location 108. If thefastening tool or driver 30 is not in position, then the fastening toolis disabled 110. If, however, the driver 30 is in position in front ofone of the fastening locations as indicated by one of the six targets,then the fastening tool is enabled 112. The driver torque may then bemonitored 114. The input received from the position sensor 54 is alsoevaluated based on the differentiating characteristics of the varioustargets 50 a-50 c, 51 a-51 c to determine tool position 116 and firstwhether the tool is servicing either fixture A 18 or fixture B 19 andthen whether the tool is in the first fastening position, the secondfastening position, or the third fastening position as indicated byschematic blocks 120, 122, 124. There are similar sequences run for bothfixtures A and B as indicated, but only one sequence is for fixture A isshown to simplify the drawings.

[0042] As shown, once the tool fastening position is determined, thenthe electronic controller 58 determines whether the torque value hasbeen reached for that position as indicated by schematic blocks 126,128, and 130. If the torque value has been reached as previouslymonitored in schematic block 114, then a torque flag is set representingthat fastening location as indicated in schematic blocks 132, 134, 136.Thereafter, all torque flags are monitored 138 to determine whether allthree torque flags representing the three different fastening locationshave been set 140. If all torque flags have been set, then the fixtureis allowed to leave the station 10 and all of the flags for fixture typeA are reset 142 and the system can be recycled 144. If however, not allthree torque flags have been set 140, then the entire process isrecycled back to the beginning and the fixture position is again sensed100.

[0043] It will be appreciated that all of the operations indicated inFIG. 5 from start to end take only a fraction of a second and therefore,this cycle may be run tens or hundreds of times every second to updatethe torque values indicated in blocks 132, 134, and 136 on aninstantaneous basis. It will also be appreciated that with thecontinuous type system that two different types of fixture targets neednot be supplied if the fixtures 18, 19 are sufficiently spaced apartsuch that only one fixture occurs over the working span 16 of theassembly station 10 at any given time or that it is unlikely that aworker would switch between the seats held by leading and trailingfixtures. A further advantage of having two different types or sets oftargets 50 a-50 c and 51 a-51 c is that different types of seats withdifferent fastening requirements may be run through the station on thesame continuous line if desired. Currently this is not practiced andeach line is dedicated to a single model or type of seat 12. It willalso be appreciated in viewing FIG. 4 that the general logic used in theelectronic controller is indicated and that the exact sequenceillustrated in FIG. 4 is not necessarily required. However, FIG. 4represents the various electronic connections of the electroniccontroller 58 and the determinations and inputs and outputs conducted bythe electronic controller 58.

[0044] Further features may also be added. For example, a furtherfeature that can be used which is not illustrated in FIG. 4 is that oncea flag is achieved for one of the given fastening locations 52 a-c, thedriver 30 may be disabled when it is indicated the driver 30 is in frontof that position. This prevents a worker from operating the driver inreverse and removing a properly fastened bolt. the electronic controller50 may also or alternatively have a predetermined sequence programrequiring a predetermined sequence of fastening among the fasteninglocations 52 a-c. According to this feature, the electronic controllercontrols the sequence of fastening based upon the target output andprovides a sequence output indicating whether the predetermined sequencehas been achieved. This may simple entail ensuring that the driver 30 isactive only when in front of the correct one of the fastening locations52 a-c as indicated by the respective targets 50 a-c.

[0045] Turning then to FIG. 5, a control and flow diagram for anintermittent conveyor system is illustrated whereby seat fixtures 200would be stopped at the assembly station while the work operations areperformed at that station and not released until all work operationshave been successfully completed. According to this system, theelectronic controller monitors fixture position 202 based on output froma fixture position sensor 204 which indicates whether or not the seatfixture 200 has arrived at a fixed stopped position along theintermittent conveyor system (not shown). The system determines firstwhether the fixture 200 is in place 206. If the fixture 200 is not inplace, then the fastening tool 208 is disabled 210 and the cycle isrestarted. Once the fixture, however, is in place, then the output froma tool position sensor 212 is monitored 214. In particular, the toolposition sensor 212 senses one of three targets 213-215 provided on theseat fixture 200. Each of these targets 213-215 has a differentcharacteristic such that the output provided by the tool position sensor212 has a different characteristic that can be monitored 214 by theelectronic controller. Because the fixture is in place 206, thefastening tool may be enabled 216 (or alternatively enablement of thefastening tool may depend upon whether the fastening tool 208 is at aproper fastening location as indicated by the tool position sensor 212).The electronic controller then monitors torque 218 as indicated by thetool torque monitor 220 of the fastening tool 208. Based on the sensedposition sensor input from the tool position sensor 212, the electroniccontroller can then interpret the position sensor input to determine thetool position 222 to determine whether it is positioned to fasten afastener at one of the three fastening locations. Thereafter, dependingupon whether the tool is in fastening position one, two, or three223-225, the electronic controller will compare the monitored torque 218to a predetermined torque value 227-229 and if appropriate set a torqueflag 230-232 for the first to third fastening locations, respectfully.The electronic controller monitors all torque flags 235 to determinewhether appropriate torque values for all three fastening locations hasbeen set 237. If so, the torque flags may be reset 239 the fasteningtool disabled 241 and the conveyor can be activated to move the fixtureholding the seat out of the assembly station 243, and the process can bestarted again once a new seat and seat fixture 200 enter the assemblystation. If, however, not all three torque flags have been set 237, thenthe process is recycled to again run through each of the steps until allthree torque values have been reached as indicated by the torque flags230-232 thereby indicating that all work operation have been properlyperformed and that the seat and fixture are ready for further downstreamwork operations if appropriate.

[0046] The target and target sensor assembly of the system isillustrated in FIG. 6. As shown, the targets may comprise two bolts atdifferent angular orientations among the various targets 50 a, 50 b, 50c. The machine vision camera 54 has an output representing the targetsthat can be interpreted by the electronic controller 50 and used fordifferentiation determinations. Although two different geometric shapeshave been illustrated as the targets, it will be appreciated that thetargets may be selected from the group consisting of geometric shapes,colors and alphanumeric characters.

[0047] A second embodiment of a sensing system is shown in FIG. 7.According to this system a laser emitter and receiver device 300 isutilized in association with reflective panel(s) which may includeseparate panels or a single inclined reflective panel 302 asillustrated. According to this embodiment, the individual targets 304comprise spaced apart sections of the reflective material which are atdifferent distances along the plunging axis relative to the emitter andreceiver device 300. Because reflection and distance among the plungingaxis is critical for this embodiment, as the fastening tool plungesalong a fastening axis, the laser and laser sensing device remainingstationary during plunging of the fastening tool to keep the targets 304at the desired distance from the laser emitter and receiver device 300.

[0048] It should be noted that a minimum of two different fasteninglocations and targets as described above are necessary for the subjectinvention. It will readily be appreciated to those skilled in the artthat any number of targets and fastening locations above two may be usedand are specifically intended to be covered by all of the claimsappended hereto.

[0049] It should also be noted that the present position monitoringsystem may also incorporate a sensor, linear transducer or laser tomonitor the tool position to determine bolt position in the verticalaxis 26. For example, bolts on the seats carried on the conveyor arealways at a constant known elevation. As such, if bolts are at differentelevations, and, if a fixed angle, 90 degree driver/tool is being used(rather than a tool that pivots), then sensing tool elevation providesan indication of the particular bolt being serviced. This may also beused to determine cross line or plunging travel of the tool in theplunging axis 28, and thus used to differentiate bolts spaced atdifferent spacing in the plunging axis 28. The electronic controller 58may use feedback from such tool position sensors to determine thefastening location being serviced in addition to the target sensingsystem feedback.

[0050] Although a laser sensor and machine vision camera sensor havebeen shown in FIGS. 6 and 7 of a preferred embodiment, it will beappreciated that other sensors and targets may also be utilized and arecovered by certain claims appended hereto. For example, a bar codescanner could act as the sensor with bar codes used for targets.

[0051] The disclosed position system can also be used to set differentparameters for each bolt. The parameters include run down speed,acceleration, deceleration, and the final torque target value. This isvaluable because it helps to proactively prevents bad run downs whichslow down the assembly process.

[0052] All of the references cited herein, including patents, patentapplications, and publications, are hereby incorporated in theirentireties by reference.

[0053] The foregoing description of various embodiments of the inventionhas been presented for purposes of illustration and description. It isnot intended to be exhaustive or to limit the invention to the preciseembodiments disclosed. Numerous modifications or variations are possiblein light of the above teachings. The embodiments discussed were chosenand described to provide the best illustration of the principles of theinvention and its practical application to thereby enable one ofordinary skill in the art to utilize the invention in variousembodiments and with various modifications as are suited to theparticular use contemplated. All such modifications and variations arewithin the scope of the invention as determined by the appended claimswhen interpreted in accordance with the breadth to which they arefairly, legally, and equitably entitled.

What is claimed is:
 1. A method for assembling an article of assembly,the article of assembly having a plurality of fastening locationsincluding first and second fastening locations in spaced apart relation,comprising: holding the article of assembly in a predetermined position;providing a plurality of targets including at least a first target fixedrelative to the article of assembly corresponding to the first fasteninglocation of the article of assembly and a second target fixed relativeto the article of assembly corresponding to the second fasteninglocation, the second target having a different characteristic than thefirst target; manually fastening fasteners into the article of assemblyat the first and second fastening locations; and sensing the first andsecond targets when said fastening is occurring at the first and secondlocations, respectively, and generating an electronic target outputbased upon said sensing that differentiates between the first and secondtargets thereby indicating when the fastening tool is in either of thefirst and second fastening locations.
 2. The method of claim 1 furthercomprising conveying the article of assembly through an assemblystation.
 3. The method of claim 2 further comprising: intermittentlystopping the article of assembly at the assembly station for saidfastening; and monitoring the location of said fastening to ensureproper fastening of fasteners at the fastening locations.
 4. The methodof claim 3 further comprising: maintaining the fixture at the assemblystation and not releasing the fixture for further conveying out of theassembly station until the fastening tool has properly fastenedfasteners into the article of assembly at the first and second fasteninglocations.
 5. The method of claim 4, wherein the fasteners are threadedfasteners, further comprising: measuring torque applied to thefasteners; electronically indicating measured torque applied to thefasteners at at least one of the fastening locations; determining thelocation of said fastening that corresponds to the indicating ofmeasured torque; electronically comparing measured torque withpredetermined torque values for the at least one of the fasteninglocations; and providing an output indicating whether the predeterminedtorque values for at least one of the fastening locations have beenreached.
 6. The method of claim 6, further comprising: releasing thearticle of assembly and conveying the article of assembly out of theassembly station when the predetermined torque values have been reached.7. The method of claim 1, further comprising: monitoring a sequence ofsaid fastening; electronically comparing the monitored sequence with apredetermined sequence of fastening among the fastening locations; andproviding a sequence output indicating whether the predeterminedsequence has been achieved.
 8. The method of claim 2 further comprisingtransporting the articles of assembly through the assembly stationsubstantially without stopping on a continuous basis.
 9. The method ofclaim 8, further comprising: providing at least two types of first andsecond targets, each different type corresponding to one of the articlesof assembly; generating said target output signal that differentiatesbetween the at least two types of first and second targets; andelectronically determining the article of assembly subject to saidfastening by differentiating between the different types of the firstand second targets.
 10. The method of claim 8 wherein the assemblystation has an input location receiving fixtures from an upstreamstation and an output location delivering fixtures to a downstreamstation, wherein said fastening is conducted in a range between theinput location and the output location, further comprising:electronically sensing when articles of assembly are exiting theassembly station and providing a fixture position output indicating whenfixtures have exited the assembly station through the output location;electronically determining whether said fastening has been properlyconducted on each article of assembly exiting the assembly station; andoutputting an electronic alarm signal when one of the articles ofassembly has exited the assembly station without proper fastening at thefirst and second fastening locations.
 11. The method of claim 10,further comprising temporarily stopping the conveying of the articles ofassembly in response to the electronic alarm signal so corrective actionmay be performed on the article of assembly.
 12. The method of claim 10,wherein the fasteners are threaded fasteners, wherein said properfastening comprises: measuring torque applied to the fasteners;electronically indicating measured torque applied to the fasteners at atleast one of the fastening locations; determining the location of saidfastening that corresponds to the indicating of measured torque;electronically comparing measured torque with predetermined torquevalues for the at least one of the fastening locations; and providing anoutput indicating whether the predetermined torque values for at leastone of the fastening locations have been reached.
 13. The method ofclaim 10 wherein said proper fastening comprises: monitoring a sequenceof said fastening; electronically comparing the monitored sequence witha predetermined sequence of fastening among the first and secondfastening locations; and providing a sequence output indicating whetherthe predetermined sequence has been achieved.
 14. The method of claim 10further comprising: assigning adjacent articles of assembly differenttypes of the first and second targets for purposes of differentiationaccording to a predetermined fixture sequence; determining the articleof assembly subject to fastening operations based upon the predeterminedsequence.
 15. The method of claim 1 wherein said sensing is accomplishedwith a machine vision camera and wherein the targets have differentvisual characteristics, further comprising electronicallydifferentiating between the different visual characteristics containedin the electronic target output to determine the location of thefastening tool.
 16. The method of claim 15 wherein the targets areselected from the group consisting of geometric shapes, colors andalphanumeric characters.
 17. The method of claim 2 wherein said sensingis accomplished with a laser and laser sensing device, said fasteningbeing accomplished with a fastening tool movable in a plane spaced fromthe article of assembly to selectively position the fastening tool atthe fastening locations, the laser and laser sensing device beingmovable with the fastening tool in said plane, the targets comprisingreflective material spaced at different distances perpendicular to saidplane.
 18. The method of 17 wherein the fastening tool plunges along afastening axis perpendicular to said plane, the laser and laser sensingdevice remaining stationary during plunging of the fastening tool. 19.The method of claim 18 wherein the article assembly is carried by aconveyor, the fastening tool being movable horizontally relative to theconveyor, the laser and laser sensing device being restricted tohorizontal movement along a horizontal axis along with the fasteningtool, further comprising a reflective panel extending in the horizontalaxis in reflective communication with the laser and laser sensing devicewith a reflective surface aligned at an oblique angle relative to saidplane providing the targets.
 20. The method of claim 1 wherein thearticle of assembly comprises an automotive seat comprised of at leasttwo parts, the fasteners comprising threaded fasteners for fastening theat least two parts together.
 21. The assembly system of claim 1 furthercomprising: enabling the fastening tool when one of the targets issensed; and disabling the fastening tool when none of the targets aresensed.
 22. A method for assembling an article of assembly, the articleof assembly having a plurality of fastening locations including firstand second fastening locations in spaced apart relation, comprising:holding the article of assembly in a predetermined position; manuallyfastening fasteners into the article of assembly using a fastening toolat the first and second fastening locations according to a predeterminedfastening sequence; sensing the position of the fastening tool;electronically comparing the sensed position of the fastening tool witha predetermined sequence of fastening among the first and secondfastening locations; and providing a sequence output indicating whetherthe predetermined sequence has been achieved.
 23. The method of claim22, wherein the article of assembly comprises a vehicle seat.
 24. Themethod of claim 22, further comprising enabling the fastening tool whenthe fastening tool is at one of the first and second locations and apredetermined fastening sequence is followed, and disabling thefastening tool when the predetermined fastening sequence is notfollowed.
 25. The method of claim 24, further comprising disabling thefastening tool when not at a fastening location.
 26. The method of claim24, further comprising monitoring torque applied during said manualfastening, providing an electronic torque output indicating whether atleast one predetermined torque value has been reached.
 27. The method ofclaim 26, enabling the fastening tool when the fastening tool is at oneof the first and second locations and a predetermined fastening sequenceis followed, and disabling the fastening tool when the predeterminedfastening sequence is not followed.
 28. The method of claim 27, furthercomprising disabling the fastening tool when a predetermined torquevalue is not reached for one of the fastening locations in thepredetermined sequence and the fastening tool is at a fastening locationother than said one of the fastening locations.
 29. The method of claim22, wherein said sensing comprises sensing targets including first andsecond targets arranged in relation to the first and second fasteninglocations, the first and second targets being sensed when said fasteningis occurring at the first and second fastening locations, respectively;and generating an electronic target output based upon said sensing thatdifferentiates between the first and second targets thereby indicatingwhen the fastening tool is in either of the first and second fasteninglocations.
 30. The method of claim 29, wherein said sensing is conductedwith one of a machine vision camera and a laser sensing device.